Power tool housing

ABSTRACT

A housing for an electric tool has a plurality of spring arms for exerting a spring force on a brush holder that holds a brush for engaging a commutator. Preferably, the spring arms are integral with a tool housing end cap.

FIELD OF THE INVENTION

[0001] The present invention is related to power tools, as well as tohousings for power tools.

BACKGROUND OF THE INVENTION

[0002] Electric power tools such as portable electric drills, circularsaws, jigsaws, sanders, and the like are widely known in the art.Generally, they include an electric motor for rotatably driving a shaft,with a tool such as a drill bit, a saw blade, or the like attached tothe shaft. The electric motor is often an AC or DC motor that includes arotating armature with a commutator. Two non-rotating conducting brusheselectrically contact the commutator. The motor assembly, including thearmature, the commutator and the brushes, is enclosed in a housing. Thebrushes must be urged into engagement with the commutator with a springto ensure good contact with the, provide some degree of tolerance, andalso compensate for wear of the brush.

[0003] Because electrical current flows through each of the brushes,they are often movably held in an insulating brush box or holder. Thebrush holder insulates the brush from the housing. The spring whichbiases the brush into engagement with the commutator is typicallycontained in the brush holder, and the brush (or the spring) iselectronically connected to have a power source such as an AC supply ora DC battery.

[0004] During manufacture of such tools in the prior art, the motorarmature and commutator were provided pre-assembled, and installed inthe housing at the time of final tool assembly. Each brush and brushholder were likewise provided as a pre-assembled unit and installed inthe housing at the time of final tool assembly. To speed and simplifytool assembly, the brush holder may have been installed through an openend of the housing by placing it in a bracket that has been pre-formedin the housing. To retain the brush holder in place in the bracket, ahousing end cap had either a brush holder locking assembly extendingtherefrom, so that when the end cap was attached to the housing, theholder locking assembly locked the brush holder in place, or a screw orscrews that secure the brush holder to the housing.

[0005] To allow for some tolerance in housings and brush holders, and toprovide for long service life of the tool, the brush holder lockingassembly included a spring member such as a rubber-like polymer layer orpad for engaging the brush holder. By way of particular example, oneknown tool assembly included a housing end cap having a hollow brushassembly support tube connected thereto. A resilient polymer bumper padwith a barrel portion was inserted into the hollow tube, and had a brushholder-engaging portion that engaged the brush holder. The bumper padheld the brush holder in place, and also provided a degree of protectivecushion to the holder to prevent holder breakage if the tool was droppedon its end cap. This known configuration, however, was time consuming toinstall in the housing.

[0006] The commercial market for such tools is competitive, with a largenumber of competitors vying for market share. In this competitiveenvironment, there are strong business incentives to keep manufacturingcosts low. Accordingly, it is desirable to reduce the number of partsand the number of steps required to manufacture the tools.

[0007] These and other needs remain unresolved in the art.

SUMMARY OF THE INVENTION

[0008] One exemplary embodiment of the present invention is directed toa tool housing for a tool of the type that has a rotating electric motorwith brush holders for holding brushes. An exemplary housing of theinvention comprises a housing wall and a plurality of spring armsconnected to the wall, the spring arms being configured to springinglyengage each of the brush holders.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a perspective view, partially cutaway, of an exemplarytool housing of the invention;

[0010]FIG. 2 is a perspective view of the end cap of the housing of FIG.1;

[0011]FIG. 3 is a cross sectioned view of the housing end cap of FIG. 2viewed along the line 3-3 in the direction generally indicated and inengagement with a brush holder;

[0012]FIG. 4 is a cross sectioned view of the housing end cap of FIG. 2viewed along the line 4-4 in the direction generally indicated and inengagement with a brush holder;

[0013]FIG. 5 is a perspective view of an exemplary brush holder; and,

[0014]FIG. 6 is a perspective view of an exemplary tool housing of theinvention with the end cover removed.

DETAILED DESCRIPTION

[0015] An exemplary embodiment of the present invention is directed toan electric power tool housing shown generally at 10 in FIG. 1. Thehousing 10 generally includes a removable end cap 12 and a main bodyportion 14. As best illustrated by FIG. 2, the end cap 12 has aplurality of integral spring arms 16. The term “integral” as used hereinis intended to broadly refer to a general condition of beingsubstantially continuous with. By way of example, as used herein twoparts that were formed as a unit with one another would be integral. Inthe preferred housing end cap 12, the arms 16 and the end cap 12 arepreferably formed of injection molded plastic in a single moldingprocess, and are therefore integral with one another. Other formationmethods are contemplated, however, as are spring arms 16 that are notintegral with an end cap 12.

[0016] The end cap 12 further includes a ventilation grate 18 and aplurality of fastener receiving passages 20. The passages 20 may receivea fastener such as a threaded bolt or the like used to attach the endcap 12 to the housing main body 14, with FIG. 1 showing the end cap 12installed. Although the preferred housing end cap 12 is removable fromthe housing main body 14, other invention embodiments may include ahousing 10 with a permanently attached end cap 12. A removable cap 12 ispreferred, however, for reasons such as ease of assembly, servicing ofthe tool, and the like.

[0017] As best illustrated by FIGS. 1, 3 and 4, the arms 16 areconfigured to springingly engage a brush holder 22 that supports a brush24 therein. As used herein, the term “springingly engage” is intended tobe broadly interpreted as generally exerting a spring force againstsomething. By way of example and not limitation, if a spring contacts asurface and is at least partially compressed or deflected when incontact with that surface, it is exerting a spring or biasing force andaccordingly “springingly engages” the surface. Put another way, thespring arms 16 exert a spring force on the brush holder 22. FIG. 5illustrates an exemplary brush holder 22. It generally includes at leasta carbon brush 24 that is urged in a first direction by a spring 26 heldin the brush holder 22, and a top sidewall 28. The brush 24 is forelectrically conducting contact with a motor commutator, and typicallyis, for instance, a piece of carbon that has been molded or cut from ablock or sheet.

[0018] When the end cap 12 is installed on the housing main body portion14, a plurality of the spring arms 16 springingly engage the brushholder 22 to hold it in place on a bracket 30 connected to an interiorwall 32 of the housing main body portion 14. FIG. 6 shows the housingmain body portion 14 with the end cap 12 removed. Two brackets 30 forsupporting the brush holders 22 are located across the housing main bodyportion 14 from one another. In the view of FIG. 6, one brush holder 22is in place on the rightward bracket 30, while no brush holder 48 is inplace on the opposing leftward bracket 30. The brush holder 22 is placedon the bracket 30 with the brush facing the interior of the housing mainbody portion 14.

[0019] Although no motor is present in the view of the housing shown inFIG. 6, it will be appreciated that the brackets 30 position the brushholders 22 and accordingly the brushes 24 to engage the rotatingcommutator of a motor contained in the housing 10. The main body 14further includes a motor mounting structure 34 that is useful forsupporting a motor. The mounting structure 34 includes two threadedpassages 36 that cooperate with the fastener receiving passages 20 ofthe end cap 12 to threadably receive a fastener inserted through thepassages 20 to hold the end cap 12 in place.

[0020] The brackets 30 are configured to receive and mate with the brushholders 22 to restrain the holders 22 against movement in substantiallyall directions except in the direction toward the end cap 12. That is,the brackets 30 are generally configured to contact all of the sides ofthe brush holders 22 except the top sidewall 28. In this manner thebrackets 30 support the brush holders 22 and provide restraint againstlateral movement generally along the plane of a housing main bodyportion 14 cross section. It will be appreciated that as used herein theterm “restrain against movement” is to be broadly interpreted and is notintended to confer an absolute restraint against any movement. Forexample, the brackets 30 may be configured to allow for some slightmovement in any direction to provide a degree of tolerance.

[0021] As best shown by FIGS. 1, 3 and 4, the spring arms 16 engage thebrush holder top sidewall 28 to thereby resist movement in the directiontowards the end cap 12. In particular, when the end cap 12 is installedon the housing main body 14, the substantially flat top ends 38 of thespring arms 16 engage the top sidewall 28 of the brush holder 22 to holdit in place on the bracket 30. As best shown in FIGS. 2 and 3, thespring arm top ends 38 are of a larger area than a cross section of thearms 16 so as to provide an enlarged surface area for engaging the brushholder 22. As best shown by FIG. 2, the exemplary end cap 12 includestwo opposing pairs 40 of spring arms 16 configured to engage one brushholder 22. That is, four individual spring arms 16 engage one brushholder 22. Other invention embodiments are contemplated that could use adifferent number of spring arms to engage a brush holder 22. Four armsare preferred, however, in that this number has been discovered toprovide generally secure engagement.

[0022] The spring arms 16 extend from a generally concave interior wall42 of the end cap 12. Each of the arms 16 has a generally arcuate shape,and is generally tapered from a thicker lower portion 44 to a thinnerupper portion 46. Each of the arms 16 has a first end 48 that isproximate to the shell interior wall 42 and distal from thesubstantially flat top end 38. A base 50 connects lower portions 18 ofeach individual arm 16 in each of the generally adjacent pairs 40 ofarms to one another. A bottom edge 52 of the base 50 is connected to theconcave shell interior wall 32. The base 50 is also supported by aplurality of ribs 54 that extend from the back of the base 50 to theshell interior wall 32. The preferred base 50 and the ribs 54 areintegral with the arms 16 and the end cap 12.

[0023] The spring arms 16 are configured such that they will be bentslightly as the end cap 12 is attached to the main body 14 and they comeinto contact with the brush holders 22. This bending contributes to thespring force that is developed in the arms 16 and exerted onto the brushholder 22. The arms 16 are arcuately shaped, with the arcuate shapeuseful to generally evenly distribute the stress that occurs as they arebent over the length of the arms 16. This significantly reduces localconcentrations of stress that might otherwise occur in arms of differentshapes (e.g., straight arms), and thus reduces the occurrence ofcracking in the arms 16.

[0024] Also, the generally tapered shape of the arms 16 from the thickerbase portion 44 to the thinner upper portion 46 provides a degree offlex to the arms 16 useful for developing a spring force and foravoiding cracking. These features also allow the spring arms 16 toabsorb some energy that results when the end cap 12 is impacted, andthereby to cushion the brush holders 22 against breakage that mightotherwise result from such impacts. By way of example, portable handtools are known to frequently be dropped, and often land on theirhousing end caps 10. Stiff or rigid connection between the end cap 12and the brush holder 22 when such an impact occurred could lead todamage of the brush holder 22.

[0025] Because the preferred end cap interior wall 32 has a generalconcave shape, each of the two arms 16 in each of the pairs 40 arepreferably of differing lengths. This allows the top end 38 of each ofthe arms in a pair 40 to be at substantially the same level. This isbest illustrated through consideration of FIG. 4, where H1 representsthe “height” or the extension length of the left arm 16, and H2represents the “height” or extension length of the right arm 16. Asillustrated, H1 is larger than H2 since the right arm 16 extends from a“higher” point on the concave wall 32. The two extension lengths H1 andH2 differ by an amount such that the top ends 38 of the two arms 16 areat substantially the same level. This provides for relatively evenengagement of the brush holder 22.

[0026] Each of the pairs 40 of two adjacent arms faces another of thepairs 40 so that each arm 16 generally arcs towards an opposing arm 16.As a result, the bottom portions 44 of opposing arms 16 are spaced apartfrom one another by a distance greater than the distance that separatestheir upper portions 46. In the exemplary end cap 12, four pairs 40 ofarms have been provided.

[0027] Although not illustrated in the drawings, it will be understoodby those knowledgeable in the art that housings of the present inventionwill have utility when used with portable electric hand tools such ascircular saws and the like to contain a motors for the tool. Withreference to FIG. 1 in particular, it will be appreciated that thehousing main body 14 may be attached to, for instance, a handheldcircular saw frame that included a handle, a saw guide, a base and thelike.

[0028] Housings of the present invention thereby provide many advantagesand solve several problems of the prior art. For example, housings ofthe present invention are able to substantially eliminate the need for aseparate spring member that may otherwise be required for supporting abrush holder in place. As used herein, the term “separate spring member”is intended to broadly refer to any separate member for providing springforce, with examples including rubber and rubber-like polymer pads andlayers. Embodiments of the present invention thereby achieve savings inmaterial costs and reduced assembly costs over the prior art that usedseparate spring members. Other advantages of the present invention willbe clear to those skilled in the art.

[0029] It will be appreciated that although discussion and descriptionhas been made herein of a particular tool and housing embodiment, suchtreatment has been made only to illustrate the invention. Otherinvention embodiments and equivalents to various features of theinvention as described will be apparent to those skilled in the art.

[0030] Various features of the invention are set forth in the attachedclaims.

What is claimed is
 1. A power tool housing for a power tool of the typethat has an electric motor with a rotating commutator, a plurality ofconducting brushes for contacting the rotating commutator, and aplurality of brush holders for holding the brushes, the housingcomprising: a housing wall having a support surface for receiving eachof the brush holders; and a plurality of spring arms connected to saidhousing wall, said plurality of spring arms being-configured tospringingly engage the brush holders.
 2. A tool housing as defined byclaim 1 wherein said housing includes a removable end cap and a mainbody portion, said end cap having at least one fastener passage and aventilation grate, said fastener passage for receiving a fastener forattaching said end cap to said main body portion, and wherein saidplurality of spring arms is connected to said end cap.
 3. A tool housingas defined by claim 1 wherein said plurality of spring arms is integralwith said housing wall.
 4. A tool housing as defined by claim 1 whereinsaid plurality of spring arms is arranged into a plurality of pairs ofgenerally adjacent spring arms.
 5. A tool housing as defined by claim 4,wherein two of said plurality of pairs of spring arms are arrangedfacing one another and spaced apart from one another, said two pairs ofspring arms for engaging one of the brush holders.
 6. A tool housing asdefined by claim 4 wherein each individual spring arm of said adjacentpairs of spring arms has a bottom portion, and wherein the housingfurther includes a base connecting said bottom portions from each ofsaid adjacent spring arms in one of said pairs to one another, said baseconnected to said housing wall.
 7. A tool housing as defined by claim 4wherein said plurality of spring arms includes four of said pairs of twospring arms.
 8. A tool housing as defined by claim 1 wherein each ofsaid plurality of spring arms is generally arcuately shaped.
 9. A toolhousing as defined by claim 1 wherein the brush holder has at least oneside wall, and wherein each of said plurality of spring arms have afirst end connected to said housing wall and a substantially flat topend distal from said first end for engaging the brush holder sidewall.10. A tool housing as defined by claim 1 wherein said housing shell andsaid plurality of spring arms are integral with one another and made ofinjection molded plastic.
 11. A tool housing as defined by claim 1wherein each of said plurality spring arms is generally arcuately shapedand tapered wherein a lower portion of said spring arm is thicker thanan upper portion.
 12. A tool housing as defined by claim 1 wherein saidplurality of spring arms include a plurality of pairs of two springarms, a base connecting said two spring arms in each of said pairs. 13.A tool housing as defined by claim 12 wherein each of said plurality ofspring arm pairs oppose another of said pairs of spring arms.
 14. A toolhousing as defined by claim 12 wherein each of said bases is supportedby a plurality of ribs connected to said housing wall.
 15. A toolhousing as defined by claim 1 wherein said plurality of spring arms isconfigured to exert a spring force on the brush holder without the useof a separate spring member.
 16. A tool housing as defined by claim 1wherein each of said plurality of spring arms has a generally arcuateshape, and wherein each of said plurality of spring arms are arranged toface another of said plurality of spring arms, said spring arms facingone another being arched towards one another.
 17. A tool housing asdefined by claim 1 wherein said plurality of springs arms consists ofeight spring arms, four of said spring arms being configured to engageone of the brush holders.
 18. A tool housing as defined by claim 1wherein said housing wall is generally concave shaped, and wherein saidplurality of spring arms are arranged into at least one pair of twogenerally adjacent spring arms, said two generally adjacent spring armsextending by different lengths from said concave interior wall so as toterminate at substantially the same level.
 19. A tool housing as definedby claim 1 wherein the housing includes a main body portion and aremovable end cap, wherein said plurality of spring arms are connectedto said removable end cap, and wherein said main body includes aplurality of brackets for supporting the brush holder, said spring armsconfigured to engage the brush holders when said end cap is installed onsaid housing main body and to hold the brush holders in place on saidbrackets.
 20. A hand tool housing as defined by claim 19 wherein saidbrackets are configured to restrain the brush holders from movement insubstantially all directions except towards said removable end cap. 21.A hand tool housing for a hand held tool of the type that includes anelectric motor with a rotating portion, two brushes held in two brushholders, the brushes for conductively contacting the rotating motorportion, the housing comprising: a housing main body portion having twobrackets for supporting the two brush holders; an end cap removablyattached to said housing main body portion; and, a plurality ofgenerally arcuately shaped spring arms integral with said end cap andconfigured to exert a spring force onto the brush holders when said endcap is attached to said housing main body portion, each of saidplurality of spring arms facing another of said plurality of spring armsand having a substantially flat top end for contacting one of the brushholders.
 22. A hand tool housing as defined by claim 21 wherein saidplurality of spring arms are arranged into a plurality of generallyadjacent pairs of spring arms; and wherein each of the brush holders aresupported by two of said plurality of pairs of spring arms.